Cyclic ketals and acetals of norbornane carboxyaldehyde

ABSTRACT

CHEMICAL COMPOUNDS CHARACTERIZED BY THE STRUCTURAL FORMULA   1-R4,2-R3,2-((-O-R6-O-)&gt;C(-R5)-),3-R1,3-R2-NORBORNANE   WHEREIN R1, R2, R3 AND R4 EACH REPRESENTS HYDROGEN OR METHYL, R5 REPRESENTS HYDROGEN OR LOWER ALKYL AND R6 REPRESENTS A POLYMETHYLENE RADICAL OF FROM 2 TO 4 CARBON ATOMS WHICH IS UNSUBSTITUTED OR SUBSTITUTED WITH LOWER ALKYL GROUPS HAVE VERY PLESANT, STRONG AND LONG LASTING AROMAS AND ARE ARE USEFUL AS COMPONENTS IN FRAGRANCE COMPOSITIONS. THESE COMPOUNDS CAN BE PREPARED BY AN ACETALIZATION REACTION OF AN APPROPRIATE NORBORNANE OR NORBORNENE CARBOXALDEHYDE OR AN APPROPRIATE NORBORNYL OR NORBORNENYL ALKYL KETONE WITH A DIHYDRIC ALCOHOL. THE NOVEL CHEMICAL COMPOUNDS CHARACTERIZED BY THE STRUCTURAL FORMULA   1-R4,2-R3,2-((-O-R6-O-)&gt;C(-R5)-),3-R1,3-R2-NORBORNANE   WHEREIN R1, R2, R3, R4, R5 AND R6 ARE AS DEFINED ABOVE ARE PARTICULARLY PREFERRED DUE TO THEIR OUTSTANDING USEFULNESS AS AROMA CHEMICALS.

United States Patent 3,748,344 CYCLIC KETALS AND ACETALS 0F NORBORNANECARBOXYALDEHYDE Darvin L. McCloud, Overland, and Alfred A. Schleppnik,St. Louis, Mo., assignors to Monsanto Company, St. Louis, M0. N0Drawing. Filed Dec. 27, 1971, Ser. No. 212,740 Int. Cl. C07d 13/04,15/04 US. Cl. 260-340.7 Claims ABSTRACT OF THE DISCLOSURE Chemicalcompounds characterized by the structural formula wherein R R R R R andR are as defined above are particularly preferred due to theiroutstanding usefulness as aroma chemicals.

This invention relates to the art of fragrance compositions. Morespecifically, this invention is directed to a class of compounds thatpossess characteristics aromas and are useful as components in fragrancecompositions and to a class of novel compounds possessing particularlyoutstanding characteristic aromas.

The art of Perfumery began, perhaps, in the ancient cave dwellings ofprehistoric man. From its inception, and until comparatively recently,the perfumer has utilized natural perfume chemicals of animal andvegetable origin. Thus, natural perfume chemicals such as the essentialoils, for example, oil of rose and oil of cloves, and animal secretionssuch as musk, have been manipulated by the perfumer to achieve a varietyof fragrances. In more recent years, however, research perfume chemistshave developed a large number of synthetic odoriferous chemicalspossessing aroma characteristics particularly desired in the art. Thesesynthetic aroma chemicals have added a new dimension to the ancient artof the perfumer, since the compounds prepared are usually of a stablechemical nature, are inexpensive as compared with the natural perfumechemicals and lend themselves more easily to manipulation than naturalperfume chemicals since such natural perfume chemicals are usually acomplex mixture of substances which defy chemical analysis. In contrastthereto, the synthetic aroma chemicals possess "ice a known chemicalstructure and may therefore be manipulated by the perfumer to suitspecific needs. Accordingly, there is a great need in the art offragrance compositions for compounds possessing characteristic aromas.

The principal object of the present invention is to provide a new classaroma chemical compounds.

Another object of the present invention is to provide a specific classof aroma chemical compounds having a characteristic aroma which isutilized in the preparation of fragrances and fragrance compositions.

These and other objects, aspects and advantages of this invention willbecome apparent from a consideration of the accompanying specificationand claims.

In accordance with the above objects, there is provided by the presentinvention a class of compounds characterized by the structural formula Iwherein R R R and R each represent hydrogen oi methyl, R representshydrogen or a lower alkyl and R represents a polymethylene radical offrom 2 to 4 carbon atoms which is unsubstituted or substituted withlower alkyls which, as a whole exhibits a characteristic pleasant,strong and long lasting aroma, which is highly useful in the preparationof fragrance compositions and perfumed products.

By the term lower alkyl is meant an alkyl group having from 1 to 5carbon atoms, whether branched or straight chain, such as methyl, ethyl,propyl, isopropyl, butyl, tert-butyl, pentyl and the like. Preferredlower alkyl groups are n-alkyl groups having 1 to 3 carbon atomsinclusive.

Preferred and novel compounds within the scope of Formula I arecharacterized by the structural formula a if wherein R R R R R and Rhave the same meaning as defined hereinbefore.

The compounds of the present invention, wherein R is hydrogen, arereadily prepared as hereinafter described.

In the first step, an appropriate cyclopentadiene is reacted with ana,/3-unsaturated aldehyde of the formula R R C=CR CHO wherein R R and Rare as defined hereinbefore. Illustrative aldehydes include acrolein,methacrolein, crotonaldehyde, Z-pentenal and the like.

The reaction proceeds via the Well known Diels-Alder addition to yield anorbornene carboxaldehyde compound characterized by the followingformula:

wherein R R R and R are as previously defined. The reaction conditionsof the Diels-Alder reaction are not critical, although elevatedtemperatures such as 50l50 C. are normally employed.

In the second step, the products of this invention are obtained from theabove carboxaldehyde compounds by acid-catalyzed acetalization with adihydric alcohol such as 1,2-diol, 1,3-diol or 1,4-diol.

The term 1,2-dio refers to a saturated hydrocarbon compound that has twohydroxy groups attached thereto on adjacent carbon atoms. The term1,3-diol refers to a saturated hydrocarbon compound that has two hydroxygroups attached thereto but that are attached to carbon atoms that areseparated by one carbon atom. The term IA-diol refers to a saturatedhydrocarbon compound that has two hydroxy groups attached thereto butthat are attached to carbon atoms that are separated by two carbonatoms.

Representative 1,2-diols which can be utilized in the acetalizationreaction include ethylene glycol, 1,2-propanediol, 2,3-butanediol,3,4-hexanediol, 3,4-heptanediol, 4,5- octanediol, 5,6-decanediol,6,7-dodecanediol, 2,3-dimethyl-2, 3-butanediol, 2,3-diethyl-2,3-butanediol, 3,4-diethyl-3, 4-hexanediol and the like. Representative1,3-diols which can be utilized in the acetalization reaction include1,3-propanediol, l,3-butanediol, 3-methyl-l,3-butanediol,1,3-pentanediol, 2,4-pentanediol, 3,5-heptanediol,3,S-dimethyl-3,S-heptanediol, 4,6-diethyl-2,2-dimethyl-4,6-octanediol,S-ethyI-S-methyl- 3,5-nonanediol and the like.

Representative 1,4-diols which can be utilized in the acetalizationreaction include 1,4-butane diol, 1,4-pentane diol, and 2,5-hexane dioland the like.

Acid catalysts include organic carboxylic or sulfonic acids as well asmineral acids. Organic sulfonic acids, such as benzenesulfonic acid,p-toluenesulfonic acid and the like are preferred.

The reaction conditions for the acetalization reaction are not narrowlycritical, although elevated temperatures, for example 50 to 150 C. areordinarily necessary to achieve an acceptable rate. It is also desirableto remove the water formed by the reaction as it is formed to drive thereaction to completion. This is easily efiected by conducting thereaction under reflux in a solvent, such as benzene or toluene, whichforms a minimum boiling azeotrope with water, and separating the waterfrom the distillate.

The carboxaldehyde and the dihydric alcohol which are reacted inaccordance with this invention are preferably reacted in a mole ratiofrom about 1.1 to 1 to about 1 to 1.1, however the molar ratio may befrom about 2:1 to about 1:2 and still be satisfactory. The catalyst isincluded in an amount of from about 0.01 to about 1.0 percent, based onthe weight of the reactants. Preferably, the amount of catalyst includedin the reaction is from about 100 mg. to about 500 mg. per mole ofcarboxaldehyde. Obviously the amount of catalyst added depends on theparticular reactants and the specific reaction conditions employed.

The compounds of this invention, wherein R is lower alkyl, are preparedby reacting a norbornenyl or norbornyl alkyl ketone characterized by thestructural formula wherein R R R R and R have the same meaning asdefined hereinbefore with a dihydric alcohol in a manner as hereinbeforedescribed for the carboxaldehyde compounds. Such a reaction isillustrated by the following wherein R R R R R and R have the samemeaning as defined hereinbefore.

The norbornenyl alkyl ketones can be prepared in a manner similar tothat utilized in preparing the norbornene carboxaldehydes as describedhereinbefore. In particular, an appropriate cyclopentadiene is reactedwith an tsp-unsaturated ketone of the formula:

wherein R, R, R and R are as defined hereinbefore. The reaction proceedsvia the well known Diels-Alder addition to yield the desired norbornenylalkyl ketones.

The norbornyl alkyl ketones can be prepared by suitable hydrogenation ofthese norbornenyl alkyl ketones.

The novel norbornyl compounds of this invention represented by FormulaII can be prepared by the hydrogenation of the corresponding norbornenecompound. Alternatively the norbornyl compounds can be prepared byacetalization of the norbornane carboxaldehyde obtained by hydrogenationof the norbornene carboxaldehyde or by acetalization of the norbornylalkyl ketones in a manner as described hereinbefore.

The compounds of this invention are useful in the preparation andformulation of fragrance compositions such as perfumes and perfumedproducts due to their pleasing, strong and long lasting aroma. Perfumecompositions and the use thereof in cosmetic, detergent and bar soapformulations and the like are exemplary of the utility thereof.

The novel compounds of Formula II are particularly preferred because ofthe highly desirable aroma characteristics found and the more stablechemical molecule enables a wider scope of use without fear of adverseside reactions.

The compounds of this invention are used in concentrations of from traceamounts up to about 50 percent of the perfume composition into whichthey are incorporated. As will be expected, the concentration will varydepending on the particular fragrance composition and even within thesame composition when compounded by different perfumers. The primaryconsideration being that the compound is incorporated in an odoriferousamount as desired in a particular fragrance composition.

The following examples will serve to illustrate certain specificembodiments within the scope of this invention and are not to beconstrued as limiting the scope thereof. The following standardprocedure was used for the preparations of the compounds as shown in thefollowing examples:

To a solution of 1 mole of the appropriate norbornene- (or norbornane)carboxaldehyde or alkyl ketone, in 200 ml. of benzene, containingbetween 200 to 500 mg. of p-toluene sulfonic acid is added 1.1 mole ofthe dihydric alcohol and the resulting mixture is heated to reflux withstirring until no further water is collected in a Dean- Stark trap. Theresulting reaction mixture is poured into cold, dilute sodium carbonatesolution, washed with water and concentrated sodium chloride solution,dried over sodium sulfate, filtered, followed by evaporation of thefiltrate to give the remainder as the crude product. The crude productis purified by distillation, under reduccd pressure, through a shortVigreux type column.

EXAMPLE 1 2- (5'-norbornene-2'-yl) -1,3-dioxolaneNorborn-S-en-Z-carboxaldehyde is reacted with ethylene glycol and yields68.1% of the title compound. This material has a boiling point of 89-91"C. at mm. of Hg having an n =1,4897. The product is a colorless liquid.This material was submitted to a fragrance panel for aromacharacterization and it was described as having green, cuminic, walnutand raw potato aromas.

EXAMPLE 2 2-(5-norbornene-2'-yl) -1,3-dioxaneNorborn-5-en-2-carboxaldehyde is reacted with 1,3-propanediol to givethe title compound in a yield of 28%. The boiling point of the compoundwas 126 C. at 30 mm. of Hg and having a n =1.4905. This material wassubmitted to a fragrance panel for aroma characterization and it wasdescribed as having camphoraceous, minty, styrene, cucumber andcastoreum aromas.

EXAMPLE 3 2-(norborn-2'yl)-1,3-dioxolane EXAMPLE 42-(norborn-2-yl)-1,3-dioxane Norbornane carboxaldehyde is reacted with1,3-propanediol to give the title compound in 77.5% yield. This materialhad a boiling point of 68-70 C. at 0.85 mm. of Hg having a n =l.4842.This material was submitted to a fragrance panel for aromacharacterization and it was described as havingearthy, woody, rawpotato, anise, sweet, vegetable and menthone aromas.

EXAMPLE 5 2-methyl-2- (norborn-S -en-2'-yl) -1,3 -dioxolaneNorborn-S-en-Z-yl methyl ketone is reacted with ethylene glycol to givethe title compound in a yield of 39.6%. The boiling point of thismaterial is 86 C. at 6 mm. of Hg having a n =1.4840. This material wassubmitted to a fragrance panel for aroma characterization and it wasdescribed as having pungent, animal, woody, minty and eucalyptol aromas.

' EXAMPLE 6 2-(norborn-5'-en-2'-yl)-5,5-dimethyl-1,3-dioxaneNorborn-5-en-2-yl carboxaldehyde was reacted with2,2-dimethyl-1,3-propanediol to obtain the title compound in a yield of62.5%. This material had a melting point of 65 C. and a boiling point at86 C. at 1.2 mm. of Hg. It is found to be soluble in benzene. Thismaterial was submitted to a fragrance panel for aroma characterizationand it was described as having a cucumber, green, castoreum, rancid andmilk-barn aromas.

6 EXAMPLE 7 2-methyl-2-(norborn-2-yl) -1,3-dioxolane The double bond ofnorborn-5-en-2-yl methyl ketone is hydrogenated to obtain thecorresponding norbornyl methyl ketone over palladium on charcoal.Norbornyl methyl ketone is reacted with ethylene glycol to obtain thetitle compound in a yield of 69.6%. The resulting product has a boilingpoint of 65 C. at 3.5 mm. of Hg having an n =1.4775. This material wassubmitted to a fragrance panel for aroma characterization and it wasdescribed as having eucalyptus, woody, pine, menthone, green and fecalaromas.

EXAMPLE 8 2-(norborn-2-yl)-5,5-dimethyl-1,3-dioxane Norbornylcarboxaldehyde is reacted with 2,2-dimethyl-1,3-propanediol to obtainthe title compound in an 82.4% yield. This material has a melting pointat 73 C. and was a solid, white material at room temperature. Thismaterial was submitted to a fragrance panel for aroma characterizationand it was described as having, fruity, apple, winey, ras'berry, aceticand butter aromas.

While the invention has been described herein with regard to certainspecific embodiments, it is not so limited. It is to be understood thatvariations and modifications thereof may be made by those skilled in theart without departing from the spirit and scope of the invention.

The embodiments of this invention in which a particular property orprivilege is claimed are defined as follows:

1. A compound characterized by the structural formula wherein R R R andR each represent hydrogen or methyl, R represents hydrogen or a loweralkyl and R represents a polymethylene radical of from 2 to 4 carbonatoms which is unsubstituted or substituted with no more than four loweralkyls of from 1 to 3 carbon atoms.

2. A compound as defined in claim 1 which is2-(norborn-2'-yl)-l,3-dioxolane.

3. A compound as defined in claim 1 which is 2-(norborn-2'-yl)-1,3-dioxane.

4. A compound as defined in claim 1 which is Z-methyl-2- (norborn-2'-yl)-1,3-dioxolane.

5. A compound as defined in claim 1 which is 2-(norborn-2-yl)-5,5-dimethyl-1,3-dioxane.

References Cited UNITED STATES PATENTS 3,455,955 7/ 1969 Chang 260-340.93,542,810 11/1970 Roudabush et al. 260-340.9 3,625,977 12/1971 Hamb260-340.7 3,679,756 7/1972 Kretschmar et a1. 260-3409 ALEX MAZEL,Primary Examiner I. H. 'I URNIPSEED, Assistant Examiner US. Cl. X.R.

